1. Field of the Invention
The present invention relates to an apparatus and method for detachment of the edge portion of glass sheets along a cut-off line or score previously traced on the glass sheet. The apparatus and method of the invention has particular application in the manufacture of a window, such as a windshield, rear and side window for an automobile, which may have any desired shape.
2. Description of the Prior Art
It is well known that strips of glass may be detached along a cut-off line or score which is rectilinear without any great difficulty, but problems oftentimes are encountered when it becomes necessary to both automatically and effectively detach strips of glass along a cut-off line or score which, rather than being rectilinear, may be closed and have, for example, a plurality of rectilinear or substantially rectilinear portions connected by corners which may be rounded or sharp.
In an automated production line for manufacturing automobile windows, the detachment unit is situated upstream from the finishing unit at which the edges of the windows may be ground prior to, for example, tempering operations. The detachment operation must, therefore, be effected rapidly in order to adequately supply one or often several automated finishing units. The detachment operations must, moreover, be reliably performed so that a sheet of glass with unbroken or partially broken edge portions does not reach the grinder which operates within relatively limited conventional tolerances. The detachment operation, furthermore, must provide sharp, clean edges without chips or microfissures. To this end, during the tempering operations, such edge faults form starting points for breakage of the window.
When the detachment operation is carried out improperly, it is sometimes possible to continue grinding the edges of the glass until these faults disappear. However, such an operation is both time-consuming and costly due to the additional wear on the diamond-tip grinding element.
Apparatus for and methods of detaching the edges from a sheet of glass along the periphery of a cut-off line or score automatically, rapidly, with good quality, and with complete reliability previously have been proposed in patents assigned to the assignee of the present application. Such apparatus including the use of mechanical devices for detachment of the edges from a sheet of glass are disclosed, for example, in French Pat. Nos. 1,370,508 and 1,465,518; and in U.S. Pat. Nos. 3,137,426, 3,178,085, 3,259,286, 3,300,112 and 3,770,173. The first of the noted French patents discloses mechanical devices in the form of hammers to tap the edges of the sheet of glass in the vicinity of the cut-off line or score until the edge portions detach from the sheet of glass. Aside from the last-mentioned U.S. patent, the other patents disclose rollers or the like for exerting pressure on one or both surfaces of the sheet of glass and at one or both sides of the cut-off line or score. The last-mentioned patent additionally discloses abutments which come in contact with the edges of the sheet of glass to be detached.
The mechanical devices as generally described above often produce faults during the detachment of the edges from the sheet of glass and, accordingly, these devices are not totally compatible with automatic and subsequent tempering. Additionally, it has been found to be difficult to produce, with mechanical devices of the type generally described above, windows of certain shapes, particularly windows of trapezoidal shape. Moreover, it has been found difficult to effectively detach the edges from sheets of glass having certain thicknesses.
A more recent attempt in detaching of edges from a sheet of glass is disclosed in U.S. Pat. No. 4,033,490, also assigned to the assignee of the present invention. The apparatus disclosed therein has been found to obviate the disadvantages of the prior art and functions to detach the edges from a sheet of glass by combining an application of heat to produce a clean, sharp break along at least a part of the cut-off line or score with a subsequent mechanical detaching operation to break off the edges which were not detached by heating. The application of heat is described as being provided by gas blow pipes located in the region of the corners of the window and disposed at an angle toward the side of the sheet of glass such that the flame from the blow pipe heats the edge to be detached. The mechanical operation is carried out as a second step and accomplished by means of U-shaped pincers which are disposed so that upon elevation of the sheet of glass the pincers overlap the edge of the sheet of glass and act upon it to deflect or bend it about the cut-off line or score. The apparatus including both thermal and mechanical means has been found to provide good cut-off quality. Thus, the edges are clean, with no chips and with no microfissures which may constitute a start or a break at the time of tempering. Further, the thermal and mechanical means provide complete reliability in that edges which are not detached by the action of the blow pipes alone are detached by the action of the U-shaped pincers.
The aforementioned thermal and mechanical means have been found to provide complete satisfaction when used for quantity production of the same window. However, if the type of window to be fabricated requires frequent change, the adjustment time vis-a-vis the operating time becomes too great. Hence, in the fabrication of a laminated windshield, the bending of the two sheets of glass intended to be joined is done on a form borne on a carriage. A form adapted to each type of windshield and one form per windshield are necessary. To limit the number of carriages corresponding to a given type, the train of carriages in use for bending is made up of a succession of different carriages. This requires finishing windows of all the types and, hence, both frequent changing of the cut-off line or score and resetting of the detachment devices for each change. These adjustments require an excessive time which adds to the overall cost of the procedure for fabricating a window.